This invention relates to a read-write processing apparatus for carrying out non-contact communications with an RFID tag containing a semiconductor memory to read out or write data from or into this memory and a read-write method that is carried out by such an apparatus.
Systems having a memory medium storing various data attached to each article to be transported and being adapted to read and write data from and into this memory medium by wireless communications are coming to be introduced into control sites of cargoes and assembly lines of factories. Such a system is referred to as an RFID (radio frequency identification) system and the aforementioned memory medium to be attached to each article to be transported contains an IC chip containing a semiconductor memory and a communication antenna coil and is commonly referred to as an RFID tag or a non-contact IC tag.
Prior art read-write processing apparatus for an RFID system are structured as a reader-writer having both an antenna part and a control unit inside a same housing structure, as a controller separate from an antenna part or as a controller that contains the transmission-reception circuit and the control part of the antenna part. Both when reading and writing data, prior art read-write processing apparatus are adapted to transmit a command of a specified format to an RFID tag and to receive from the RFID tag a response to this command. When an RFID tag without containing an inner power source is used, an induced electromotive force is generated in the antenna coil on the side of the RFID tag by means of transmission waves from the antenna part such that a control circuit inside the RFID tag will be driven.
With an RFID system as described above, there is a high probability that various kinds of noise will come to be mixed in the communication region for the tag and the antenna part so as to cause communication errors since the system is often introduced in an environment where machines and apparatus of various types are installed. For this reason, it is necessary to carry out test communications prior to actual system operations and to thereby check whether or not the system is in a condition capable of carrying out communications with RFID tags without any trouble.
In view of the above, the present applicant has earlier proposed a read-write processing apparatus provided with a test mode in which a read-write process is carried out and the distance to the tag is adjusted, and a display light is switched on if a communication error occurs. (See Japanese Patent Koho 2,610,897).
By the invention of aforementioned Japanese Patent Koho 2,610,897, the user can conclude that the antenna part and the RFID tag are in a condition for communicating to each other if this display light is not lit. When such an RFID system is put in an actual use in a real situation, however, there is a possibility of a communication error due, for example, to a sudden occurrence of noise, say, because of the operations of surrounding machines. It is difficult to predict, however, when and how such sudden noise may occur and the real situation is that no sufficient measure is being taken against noise.
In view of this, Japanese Patent Koho 9-190518 discloses a method according to which the read-write processing apparatus transmits to the RFID tag a command to request for the transmission of a pseudo random signal and correlation values are obtained with two kinds of reception signals to this command (signals with data arrangement similar to and not similar to that of the transmission signal from the RFID tag). Only if the correlation value C1 with the signal similar to the transmission signal is greater than a first threshold value T1 and the correlation value C2 with the signal not similar to the transmission signal is less than a second threshold value T2, an access is allowed for reading out data.
According to the invention of aforementioned Japanese Patent Koho 9-190518, reliability of communication process can be improved because actual communication can be started only after it is ascertained that the noise level is low. This invention has problems, however, in that the process becomes complicated because special communications must be carried out between the read-write processing apparatus and the RFID tag for checking the status of noise and that the read-write processing apparatus is required to carry out two correlation calculation processes. Under a circumstance where the variations of noise are large, furthermore, although a communication process may be started after it is ascertained that the two correlation values C1 and C2 both satisfy the aforementioned conditions, there may arise a sudden change in the noise and a communication error may result.
Moreover, communication errors are not limited to be caused by noise but may be caused also for reasons other than noise such as a fault in the RFID tag. In the situation of a communication error, prior art systems inclusive of those according to aforementioned Japanese Patents Koho 2,610,897 and 9-190518 are not adapted to check whether or not it was caused by noise.